Physiology - Chapter 15: The Immune System

Innate Immunity

Immunity you were born with.

• Rapid Response

• All animals have it

Adaptive Immunity

The result of previous exposure to specific pathogens (either by contracting the illness or by vaccines (immunization).

• Only found in vertebrates

• Slower response

Barrier Defense: Skin (Innate Immunity)

First line of barrier defense

• It continuously sheds, removing microbes that gain a foothold on skin.

• Skin secretions contain natural antibiotics

• Skin is acidic and has lysozyme.

Barrier Defense: Mucous membrane (Innate Immunity)

Mucous is secreted and used to trap microbes before they can enter your body.

• Cilia (tiny hairs) that physically sweep microbes from your respiratory tract causing you to cough, sneeze, etc.

Internal Defenses: Phagocytes (Innate Immunity)

Second line of defense for Innate Immunity. Phagocytosis ingests invading microorganisms by certain types of white blood cells.

4 types of phagocytic white blood cells:

1. Neutrophills

2. Macrophages

3. Eosinophilis

4. Dendritic cells

Internal Defenses: Antimicrobial Proteins (Innate Immunity)

These proteins attack microbes directly or impede reproduction.

Examples of these proteins:

• Antibodies

• Pyrogen (causes fever)

• Interferons

Interferon

Whenever a virus infects a cell, that cell releases this protein, which keeps neighboring cells from becoming infected.

• They are released by virally-infected cells

  • Helps healthy cells resist infection

  • Believed to be caused by fever

  • Activates macrophages

Internal Defenses: Inflammatory Response

Your body’s reaction to an internal infection.

• Cytokines are chemical messengers that activate other cells. A macrophage is a very large phagocytic cell. Mast cells release a chemical called histamine, which causes capillaries to become leakier so that white blood cells can exist the bloodstream more easily.

Internal Defenses: Natural Killer Cells (Innate Immunity)

These cells destroy cells that have been infected by a virus or are cancerous.

• Releases chemicals that initiate apoptosis (programmed cell death)

Acquired Immune Response

1. Recognize

2. Attack

3. Remember

Humoral Immunity (Adaptive Immunity)

Humoral means blood

• B-cells patrol the blood and destroy pathogens floating around in the bloodstream

Cell-Mediated (Adaptive Immunity)

Cell-mediated means “inside your body cells”

• T-cells destroy your own body cells that have already been infected by a pathogen.

Antigens

Any foreign molecule that is specifically recognized by lymphocytes and elicits a response from them.

• Antigen receptors are found on the surface of your immune cells

Epitope

Accessible region of an antigen to which an antigen receptor or antibody binds.

• Epitopes are found on the pathogen.

Antigen Recognition by Lymphocytes

Vertebrates have two main types of lymphocytes

• B and T lymphocytes cells both have antigen receptors on their plasma membranes.

Antibodies

These are Y-shaped molecules made of light peptide chains and heavy peptide chains.

• Antibody proteins recognize epitopes on antigens; they’re specific for each other.

• Antigens bind to the variable regions of antibodies in a lock-and-key fashion.

Major Histocompatibility Complex (MHC)

MHC proteins are found on all of your body cells. (Nametag)

• T cells must bind to an antigen presented by infected cell or antigen-presenting cell.

• Infected cells present antigen using MHC.

Class l MHC (infected- one word)

Class 1 is used by cells that have been infected, usually by a virus. Part of the viral protein gets presented on the class 1 MHC on the infected cell, and a cytotoxic T cell comes along and destroys the infected cell.

• Produced by infected body cells

• Presents to cytotoxic T cells

Class ll MHC (Antigen-presenting cells)

Class 2 is used by antigen-presenting cells, and can be recognized by both cytotoxic T cells and helper T-cells.

• This usually would be used by a phagocytic cell (macrophage) that has eaten a microbe, like a bacteria or a virus, then presented part of this microbe on its Class 2 MHC.

Clonal Selection

Once a specific B cell is found that has antigen receptors that recognize an antigen, this cell divides and makes several copies of itself to help destroy this antigen.

• This produces a lot of memory and helper T cells that help attack any future infected cells.

Helper T cells

The most important cells in the Adaptive Immune System

• Without helper T cells, both B-cells and cytotoxic T cells would have difficulty recognizing pathogens in the body.

• Helper T cells release cytokines that activate both B cells and cytotoxic T cells to fight the pathogen.

Cell-Mediated Response: Cytotoxic T cells

Cytotoxic means “destroy cells,” they destroy infected cells in your body.

• Once a cytotoxic T cell attaches to an infected body cell, it releases a protein called “perforin” which punches holes in the membrane of the infected cell.

• It then pours acid into the infected cell in the form of granzymes that dissolve the cell from inside out.

The Humoral Immune response

When a helper T cell activates a B-cell, that cell immediately divides into plasma cells and memory cells

• These plasma cells release thousands of antibodies into the blood that help neutralize the pathogen.

• Memory cells remain in the blood for the next time you encounter the pathogen.

Allergies

Exaggerated (hypersensitive) responses to antigens (called allergens)

• Allergies are the result of your immune cells becoming overly sensitive to certain substances.

• Upon exposure, your mast cells secrete massive amounts of histamine to produce the inflammatory response. (watery eyes, sneezing)

Autoimmune diseases

Conditions where antibodies and immune system cells mistakenly attack the body’s own cells

Examples:

• Insulin-dependent diabetes (Type 1 diabetes)

• Multiple sclerosis

• Rheumatoid Arthritis

AIDS is not an autoimmune disease.